What does an elevated calprotectin level in stool indicate?

Interpretation of Elevated Fecal Calprotectin of 174 μg/g

A fecal calprotectin level of 174 μg/g indicates significant intestinal inflammation that is highly suggestive of inflammatory bowel disease (IBD) or another organic inflammatory condition requiring further evaluation with colonoscopy and biopsies.

Understanding Fecal Calprotectin Values

Fecal calprotectin is a protein derived from neutrophils that indicates the presence of inflammation in the gastrointestinal tract. According to current guidelines, fecal calprotectin levels can be categorized as follows 1:

• Normal: <50 μg/g
• Borderline: 50-150 μg/g
• Elevated: >150 μg/g
• Highly elevated: >250 μg/g

At 174 μg/g, this value falls into the "elevated" category, which exceeds the borderline range and indicates active inflammation in the intestine.

Diagnostic Implications

The elevated calprotectin level of 174 μg/g has several important clinical implications:

• High sensitivity and specificity: At the 50 μg/g threshold, fecal calprotectin has a sensitivity of 81% and specificity of 87% for detecting organic intestinal disease 2, 1
• Strong differentiation from IBS: This level reliably differentiates inflammatory bowel disease (IBD) from irritable bowel syndrome (IBS) with specificity and sensitivity exceeding 85% 3
• Correlation with disease activity: The level correlates well with clinical and endoscopic disease activity in patients with IBD 4

Recommended Next Steps

1. Rule out infectious causes first:

   • Obtain stool culture and C. difficile testing to exclude infectious etiologies 1

2. Proceed to colonoscopy with biopsies:

   • Since the value is >150 μg/g, colonoscopy with biopsies is indicated to evaluate for IBD (Crohn's disease or ulcerative colitis) and other causes of intestinal inflammation 1

3. Consider potential confounding factors:

   • Check for medication use that can elevate calprotectin:
     • Proton pump inhibitors (can increase levels 3.8 times) 5
     • NSAIDs (can increase levels 2.4 times) 5
     • Aspirin/acetylsalicylic acid (can increase levels 2.9 times) 5
   • Recent colonoscopy or bowel preparation can cause false positives 1

Differential Diagnosis for Elevated Calprotectin

An elevated calprotectin of 174 μg/g could indicate:

• Inflammatory Bowel Disease:

  • Crohn's disease
  • Ulcerative colitis

• Other Inflammatory Conditions:

  • Infectious gastroenteritis (bacterial > viral)
    • Particularly Salmonella (median 765 μg/g) or Campylobacter (median 689 μg/g) infections 6
  • Microscopic colitis
  • Diverticulitis

• Neoplastic Conditions:

  • Colorectal cancer 3, 7
  • Other intestinal malignancies

Clinical Pearls and Pitfalls

• Bacterial vs. viral infections: Bacterial infections typically cause much higher calprotectin elevations than viral infections (median 89-95 μg/g for viral causes) 6

• Monitoring tool: If IBD is diagnosed, fecal calprotectin should be monitored every 3-6 months to assess treatment response 1

• Predictive value: Elevated calprotectin in patients with quiescent IBD can predict clinical relapse with >85% sensitivity and specificity 3

• Age consideration: Calprotectin levels naturally increase with age (adjusted OR: 1.051) 5

• False positives: Remember that medications (especially PPIs, NSAIDs, and aspirin), recent colonoscopy, and certain foods can cause elevated levels without significant disease 1, 5